In recent years, tumor localization by means of molecular imaging such as positron emission tomography (PET) or the like is being performed in radiation therapy. Specifically, PET imaging is performed before starting the radiation therapy, and tomographic images thus obtained are used for developing a treatment plan. It is, however, difficult for PET imaging to track the movement of a tumor in real time.
In real-time tumor tracking radiation therapy apparatuses capable of tracking the movement of a tumor in real time, on the other hand, a metal marker inserted in the patient body near the tumor is detected by a pair of X-ray fluoroscopic apparatuses and the three-dimensional position of the metal marker is calculated for controlling irradiation based on the obtained position of the metal marker.